1. Field of the Invention
The present invention relates to a wired or wireless network communication technique.
2. Description of the Related Art
In current advanced communication systems, data requiring a relatively large data communication band, for example, moving image data, is generally transmitted/received via a communication line such as the Internet.
In such transmission of moving image data requiring real-time communication, a protocol that does not compensate for a communication error, for example, RTP (Real-time Transport Protocol), is sometimes used.
In a case that sound data and moving image data are transmitted using such a protocol that does not compensate for a communication error, the prevention of occurrence of a communication error and the correction of a communication error are generally performed using a QoS (Quality of Service) technique. That is, the control of a transmission rate (rate control) is performed in accordance with a network status, the retransmission control of a communication error packet is performed, and the correction of a communication error is performed using an FEC (Forward Error Correction) technique.
A method of controlling QoS in accordance with the changes in a packet loss rate and RTT (Round Trip Time) is known. For example, Japanese Patent Laid-Open No. 2001-160824 discloses a method of reducing a data transfer rate in a case that a packet loss rate is higher than a threshold value and an RTT value is larger than the minimum RTT value stored in advance.
An example of a rate control method using a packet loss rate and RTT is disclosed in M. Handley et al., “TCP Friendly Rate Control (TFRC): Protocol Specification” RFC 3448, January 2003.
In TFRC (TCP Friendly Rate Control), an available network band is calculated using an equation illustrated in FIG. 10.
In the equation illustrated in FIG. 10, Ttcp represents an available network band to be calculated, MTU (Maximum Transfer Unit) represents the maximum size of a transmitted packet, To represents a time-out period that is the maximum waiting period before a TCP reception acknowledgement (Ack) is transmitted, and p represents a packet loss rate in 1 RTT. That is, an available band is calculated using a packet loss rate and RTT, and the calculation result is used to control a communication rate.
However, a communication error is caused by various factors. Accordingly, in some cases, QoS control may not be appropriately performed using a method in the related art.
That is, for example, a communication error is caused not only by congestion but also by noise (disturbance). The change in RTT is also caused not only by congestion but also by another factor, for example, the change in load on a receiving apparatus or a route change on a network.
If data is transmitted via a plurality of communication nodes, for example, a communication node where an error occurs and a communication node where a delay occurs may differ from each other.
That is, in some cases, the cause of a communication error occurring on a network cannot be specified using RTT and a packet loss rate. For example, even if a transfer rate is reduced in accordance with RTT and a packet loss rate when a communication error is caused by noise, the packet loss rate may not be reduced. For example, even if the number of FEC packets is increased in accordance with RTT and a packet loss rate when a communication error is caused by congestion, the amount of communication is increased and a packet loss rate may not be reduced.
That is, even if QoS control is performed in accordance with RTT and a packet loss rate obtained from a communication partner, the QoS control may not be appropriately performed.